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<?xml version="1.0" encoding="iso-8859-1"?>
<!-- $Revision: 1.5 $ -->
<!-- splitted from ./en/functions/shmop.xml, last change in rev 1.12 -->
<refentry id="function.shmop-open">
<refnamediv>
<refname>shmop_open</refname>
<refpurpose>Create or open shared memory block</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<methodsynopsis>
<type>int</type><methodname>shmop_open</methodname>
<methodparam><type>int</type><parameter>key</parameter></methodparam>
<methodparam><type>string</type><parameter>flags</parameter></methodparam>
<methodparam><type>int</type><parameter>mode</parameter></methodparam>
<methodparam><type>int</type><parameter>size</parameter></methodparam>
</methodsynopsis>
<para>
<function>shmop_open</function> can create or open a shared memory block.
</para>
<para>
<function>shmop_open</function> takes 4 parameters: key, which is the
system's id for the shared memory block, this parameter can be passed
as a decimal or hex. The second parameter are the flags that you can use:
<itemizedlist>
<listitem>
<simpara>
"a" for access (sets SHM_RDONLY for shmat)
use this flag when you need to open an existing shared memory
segment for read only
</simpara>
</listitem>
<listitem>
<simpara>
"c" for create (sets IPC_CREATE)
use this flag when you need to create a new shared memory segment
or if a segment with the same key exists, try to open it for read
and write
</simpara>
</listitem>
<listitem>
<simpara>
"w" for read & write access
use this flag when you need to read and write to a shared memory
segment, use this flag in most cases.
</simpara>
</listitem>
<listitem>
<simpara>
"n" create a new memory segment (sets IPC_CREATE|IPC_EXCL)
use this flag when you want to create a new shared memory segment
but if one already exists with the same flag, fail. This is useful
for security purposes, using this you can prevent race condition
exploits.
</simpara>
</listitem>
</itemizedlist>
The third parameter is the mode, which are the permissions that you
wish to assign to your memory segment, those are the same as permission
for a file. Permissions need to be passed in octal form ex. 0644.
The last parameter is size of the shared memory block you wish to create
in bytes.
<note><simpara>
Note: the 3rd and 4th should be entered as 0 if you are opening an
existing memory segment. On success <function>shmop_open</function> will
return an id that you can use to access the shared memory segment
you've created.
</simpara></note>
</para>
<para>
<example>
<title>Create a new shared memory block</title>
<programlisting role="php">
<![CDATA[
<?php
$shm_key = ftok(__FILE__, 't');
$shm_id = shmop_open($shm_key, "c", 0644, 100);
?>
]]>
</programlisting>
</example>
</para>
<para>
This example opened a shared memory block with a system id returned by
<function>ftok</function>.
</para>
</refsect1>
</refentry>
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